here's health and science reporter carolyn johnson. >> reporter: chris walks five miles a day just getting around his game store in downtown oakland were he knows exactly how many steps he takes thanks to a tiny tracker in his pocket called fitbit. >> it changed my life basically. >> it is one of a growing number of wearable electronics that has people wiring up to lose weight weight. >> i went to 2xl to medium and a 40-inch waist to 29-inch waist. >> he started using it two years ago. >> i hate exercising like a passion and walking to me is like exercise. >> stores have struggled to keep them in stock. >> at one point there was such a large demand they were flying off the shelf. >> two are leading the pack. job own and fitbit. both track your movement during the day and record your sleep patterns at night. they come with three apps that keep track of the calories you burn and eat. enter in what you ate on the app or scan a bar code with this app. fitbit released it's newest device last month, flex force. >> i went to 80 employees to 200 employees the past two years. products are carried i